Definition of Term: Active input

A simulator will typically have many inputs. In general, the larger the number of inputs the more complex it becomes to build a good emulator, and the larger the number of simulator runs required for the training sample. There is therefore motivation for reducing the number of inputs.

Fortunately, it is also generally found that not all inputs affect the output(s) of interest appreciably over the required range of input variation. The number of inputs having appreciable impact on outputs for the purpose of the analysis is often small. The term ‘active input’ loosely means one which does have such an impact. More precisely, the active inputs are those that are deemed to be inputs when building the emulator.